Conductive polymer dispersion liquid, electrolytic capacitor, and method for producing electrolytic capacitor

ABSTRACT

Disclosed is a method for producing an electrolytic capacitor, the method including the steps of preparing an anode foil that includes a dielectric layer, a cathode foil, and a fiber structure; preparing a conductive polymer dispersion liquid that contains a conductive polymer component and a dispersion medium; producing a separator by applying the conductive polymer dispersion liquid to the fiber structure and then removing at least a portion of the dispersion medium; and producing a capacitor element by sequentially stacking the anode foil, the separator, and the cathode foil. The dispersion medium contains water. The fiber structure contains a synthetic fiber in an amount of 50 mass % or more. The fiber structure has a density of 0.2 g/cm 3  or more and less than 0.45 g/cm 3 .

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Patent Application No. PCT/JP2020/003112, filed on Jan.29, 2020, which in turn claims the benefit of Japanese Application No.2019-016512, filed on Jan. 31, 2019 and Japanese Application No.2019-016513, filed on Jan. 31, 2019, the entire disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a conductive polymer dispersion liquid,an electrolytic capacitor, and a method for producing an electrolyticcapacitor, and more specifically to an improvement in ESRcharacteristics.

BACKGROUND ART

Capacitors for use in electronic devices are required to have a highcapacitance and a low equivalent series resistance (ESR) in a highfrequency range. An electrolytic capacitor in which a conductive polymersuch as polypyrrole, polythiophene, polyfuran, or polyaniline is used asa solid electrolyte is expected to be promising as a high capacitancecapacitor with a low ESR. Patent Literature 1 discloses a method inwhich a conductive polymer is attached to an anode foil by immersing theanode foil in a dispersion liquid that contains the conductive polymer.Patent Literature 2 discloses a method in which a conductive polymer isattached to a separator by immersing the separator in a dispersionliquid that contains the conductive polymer. By using the immersionmethods described above, the conductive polymer can be provided in thesame manner as an electrolytic solution without requiring largeequipment

CITATION LIST Patent Literatures

Japanese Laid-Open Patent Publication No. 2011-109024

Japanese Laid-Open Patent Publication No. 2015-207573

SUMMARY OF INVENTION Technical Problem

In recent years, in addition to a system (full hybrid system) that isself-movable by using only an electric motor, attention has been givento a system called “mild hybrid system” that is a type of hybrid car. Inthe mild hybrid system, an alternator that is normally mounted on apassenger car is used as an engine assisting motor. In Europe, the LV148standards that are standards for power supply have been set in which therated voltage of an alternator mounted on a passenger car is set to 12 Vto 48 V, and development has been made for practical use of the mildhybrid system.

When an alternator is configured to provide a higher voltage, anincreased amount of ripple current flows through an electrolyticcapacitor that is used together with the alternator. In order tosuppress heat generation caused by the increased amount of ripplecurrent, it is effective to use a method that reduces the equivalentseries resistance (ESR) of the electrolytic capacitor. The amount of theconductive polymer may be increased to reduce the ESR.

However, with the method described above, it is not possible to attach asufficient amount of the conductive polymer to a capacitor element. Forexample, when the concentration of the conductive polymer is increased,the viscosity of the dispersion liquid that contains the conductivepolymer also increases, which makes it difficult to cause the dispersionliquid to permeate into the inside of the capacitor element.Accordingly, as a result, the amount of the conductive polymer attachedto the capacitor element cannot be increased significantly.

Also, it is difficult to uniformly attach the conductive polymer to aseparator.

Solution to Problem

In a first embodiment of the present invention, a first aspect relatesto a method for producing an electrolytic capacitor, the methodincluding the steps of: preparing an anode foil that includes adielectric layer, a cathode foil, and a fiber structure; preparing aconductive polymer dispersion liquid that contains a conductive polymercomponent and a dispersion medium; producing a separator by applying theconductive polymer dispersion liquid to the fiber structure and thenremoving at least a portion of the dispersion medium; and producing acapacitor element by sequentially stacking the anode foil, theseparator, and the cathode foil, wherein the dispersion medium containswater, the fiber structure contains a synthetic fiber in an amount of 50mass % or more, and the fiber structure has a density of 0.2 g/cm³ ormore and less than 0 45 g/cm³.

In the first embodiment of the present invention, a second aspectrelates to a method for producing an electrolytic capacitor, the methodincluding the steps of: preparing an anode foil that includes adielectric layer, a cathode foil, and a fiber structure; preparing aconductive polymer dispersion liquid that contains a conductive polymercomponent and a dispersion medium; producing a separator by applying theconductive polymer dispersion liquid to the fiber structure and thenremoving at least a portion of the dispersion medium; and producing acapacitor element by sequentially stacking the anode foil, theseparator, and the cathode foil, wherein the dispersion medium containswater, the fiber structure contains 40 mass % or more of a cellulosefiber and a paper strengthening agent, and the fiber structure has adensity of 0.2 g/cm³ or more and less than 0.45 g/cm³.

In the first embodiment of the present invention, a third aspect relatesto an electrolytic capacitor including: an anode foil that includes adielectric layer; a cathode foil; and a separator that is interposedbetween the anode foil and the cathode foil, wherein the separatorcontains a fiber structure and a conductive polymer component that isattached to the fiber structure, the fiber structure contains asynthetic fiber in an amount of 50 mass % or more, and the fiberstructure has a density of 0.2 g/cm³ or more and less than 0.45 g/cm³.

In the first embodiment of the present invention, a fourth aspectrelates to an electrolytic capacitor including: an anode foil thatincludes a dielectric layer; a cathode foil; and a separator that isinterposed between the anode foil and the cathode foil, wherein theseparator contains a fiber structure and a conductive polymer componentthat is attached to the fiber structure, the fiber structure contains 40mass % or more of a cellulose fiber and a paper strengthening agent, andthe fiber structure has a density of 0.2 g/cm³ or more and less than0.45 g/cm³.

In a second embodiment of the present invention, a first aspect relatesto a conductive polymer dispersion liquid that is applied to asheet-like member that constitutes a capacitor element by using acoating method, the conductive polymer dispersion liquid including: aconductive polymer component; and a dispersion medium, wherein theconductive polymer component is contained in an amount of 3 mass % ormore and 15 mass % or less, and the conductive polymer dispersion liquidhas a viscosity of 100 mPa·s or more, the viscosity being measured atroom temperature by using a vibration viscometer.

In the second embodiment of the present invention, a second aspectrelates to a method for producing an electrolytic capacitor, the methodincluding the steps of: preparing sheet-like members that constitute acapacitor element; preparing a first conductive polymer dispersionliquid that contains a first conductive polymer component and a firstdispersion medium, wherein the first conductive polymer component iscontained in an amount of 3 mass % or more and 15 mass % or less, andthe first conductive polymer dispersion liquid has a viscosity of 100mPa·s or more, the viscosity being measured at room temperature by usinga vibration viscometer; forming a conductive polymer layer that containsthe first conductive polymer component by applying the first conductivepolymer dispersion liquid to the sheet-like member by using a coatingmethod and then removing at least a portion of the first dispersionmedium; and producing a capacitor element by using the sheet-like memberon which the conductive polymer layer has been formed.

In the second embodiment of the present invention, a third aspectrelates to an electrolytic capacitor including a capacitor element thatincludes: an anode foil that includes a dielectric layer; a cathodefoil; and a separator that is interposed between the anode foil and thecathode foil, wherein a conductive polymer layer that contains a firstconductive polymer component is formed on at least one selected from thegroup consisting of the anode foil, the cathode foil, and the separator,and a mass of the conductive polymer layer per unit area is 0.04 mg/cm²or more.

Advantageous Effects of Invention

According to the first embodiment of the present invention, theoccurrence of wrinkles in the separator is suppressed, and it istherefore possible to uniformly attach a sufficient amount of theconductive polymer to the separator.

According to the second embodiment of the present invention, thecapacitor element can hold a large amount of the conductive polymer.Accordingly, it is possible to obtain an electrolytic capacitor with areduced ESR.

Novel features of the present invention are set forth in the appendedclaims However, the present invention will be well understood from thefollowing detailed description of the present invention with referenceto the drawings, in terms of both the configuration and the contenttogether with other objects and features of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart illustrating an example of a method for producingan electrolytic capacitor according to a first embodiment of the presentinvention.

FIG. 2 is a flowchart illustrating an example of a method for producingan electrolytic capacitor according to a second embodiment of thepresent invention.

FIG. 3 is a side view schematically showing an electrolytic capacitoraccording to an embodiment of the present invention.

FIG. 4 is a partially exploded oblique view schematically showing aportion of the capacitor element according to the embodiment of thepresent invention

DESCRIPTION OF EMBODIMENTS

Increasing the amount of the conductive polymer can be implemented bythe first embodiment that is characterized by the separator and/or thesecond embodiment that is characterized by the conductive polymerdispersion liquid.

A. First Embodiment

Separators for electrolytic capacitors are ordinarily made of cellulose.The reason is that cellulose is low cost and can hold a large amount ofan electrolytic solution. Cellulose has a hydroxy group, and thus islikely to swell with water. For this reason, when a cellulose is broughtinto contact with a conductive polymer that has been dispersed in water,wrinkles occur instantly. It is therefore difficult to uniformly attachthe conductive polymer to the separator made of cellulose. Furthermore,swollen cellulose is likely to shrink during drying processing that issubsequently performed, and thus new wrinkles may occur. When thethickness of the separator becomes non-uniform due to wrinkles,withstand voltage and inter-electrode resistance may vary from place toplace in the electrolytic capacitor.

In the present embodiment, water, which is easy to handle, is used asthe dispersion medium for dispersing the conductive polymer component,and a fiber structure that contains a synthetic fiber in an amount of 50mass % or more, or a fiber structure that contains a cellulose fiber anda paper strengthening agent is used as the raw material of theseparator. With this configuration, the occurrence of wrinkles when theconductive polymer dispersion liquid is brought into contact with thefiber structure is suppressed. Accordingly, it is possible to obtain aseparator to which the conductive polymer component has been uniformlyattached. An electrolytic capacitor produced by using the separator haslow ESR characteristics and a uniform separator thickness, and thusvariations in withstand voltage and inter-electrode resistance aresuppressed.

Furthermore, the amount of impurities contained in the conductivepolymer component attached to the separator can be reduced as comparedwith the case where a polymerization reaction is performed on thesurface of the separator. For this reason, the withstand voltage of theelectrolytic capacitor produced by using the separator can be increased.In addition, the method for applying the conductive polymer dispersionliquid is not limited, either. It is also possible to use, for example,methods, such as a coating method and an immersion method, with which alarge amount of the conductive polymer component can be applied.

That is, in the present embodiment, the occurrence of wrinkles in theseparator during the production process is suppressed, and thus themethod for applying the conductive polymer dispersion liquid is notlimited, and a sufficient amount of the conductive polymer can beuniformly attached to the separator. As a result, the ESR of theelectrolytic capacitor is further reduced, and heat resistance is alsoimproved. Accordingly, the electrolytic capacitor according to thepresent embodiment is suitable for use in a product as described abovethrough which a large amount of ripple current flows.

B. Second Embodiment

A conductive polymer dispersion liquid according to the presentembodiment contains a conductive polymer component and a dispersionmedium, and the conductive polymer component is contained in theconductive polymer dispersion liquid in an amount of 3 mass % or moreand 15 mass % or less. The conductive polymer dispersion liquid has aviscosity of 100 mPa·s or more. By applying the high-concentrationdispersion liquid to a sheet-like member (hereinafter referred to as“constituent member”) that constitutes a capacitor element, thecapacitor element can hold a larger amount of the conductive polymercomponent than ever before.

At least a portion of the conductive polymer component is attached tothe surface of the constituent member. As a result of a sufficientamount of the conductive polymer component being attached to the surfaceof the constituent member, the ESR of the resulting electrolyticcapacitor is reduced. Furthermore, the heat resistance of theelectrolytic capacitor is also improved. Accordingly, the electrolyticcapacitor according to the present embodiment is suitable for use in aproduct through which a large amount of ripple current flows.

Furthermore, the amount of impurities contained in the conductivepolymer layer that has been formed can be reduced as compared with thecase where a polymerization reaction is performed on the surface of theconstituent member. Accordingly, it is possible to increase thewithstand voltage of the electrolytic capacitor produced by using theconductive polymer layer

Each embodiment will be described in detail.

A. First Embodiment [Method for Producing Electrolytic Capacitor]

An electrolytic capacitor according to the present embodiment can beproduced by using a method including the steps of: preparing an anodefoil that includes a dielectric layer, a cathode foil, and a fiberstructure; preparing a conductive polymer dispersion liquid thatcontains a conductive polymer component and a dispersion medium;producing a separator by applying the conductive polymer dispersionliquid to the fiber structure and then removing at least a portion ofthe dispersion medium; and producing a capacitor element by sequentiallystacking the anode foil, the separator, and the cathode foil. Note thatthe dispersion medium contains water. The fiber structure contains asynthetic fiber in an amount of 50 mass % or more, or contains acellulose fiber and a paper strengthening agent. In either case, thefiber structure has a density of 0.2 g/cm³ or more and less than 0.45g/cm³.

FIG. 1 is a flowchart illustrating an example of a method for producingan electrolytic capacitor according to a first embodiment of the presentinvention.

Hereinafter, each of the steps included in the example of the method forproducing an electrolytic capacitor according to the present embodimentwill be described.

(1) Step of preparing an anode foil, a cathode foil, and a fiberstructure (S1)

As the raw material of the anode foil and the cathode foil, for example,a metal foil that contains a valve metal is prepared.

A dielectric layer is formed on the surface of a metal foil to be usedas the anode foil. The method for forming the dielectric layer is notparticularly limited, and the dielectric layer can be formed bysubjecting the metal foil to a chemical formation treatment. In thechemical formation treatment, for example, the metal foil is immersed ina chemical formation solution such as an ammonium adipate solution, andthen heated. Alternatively, voltage may be applied to the metal foilimmersed in the chemical formation solution. A dielectric layer may beformed on the surface of a metal foil to be used as the cathode foil inthe same manner described above, or a conductive coating layer may beformed on the surface of a metal foil to be used as the cathode foil bysputtering or vapor deposition.

Prior to forming the dielectric layer and/or the coating layer, thesurface of the metal foil may be roughened, where necessary. With thesurface roughening, irregularities are formed on the surface of themetal foil. The surface roughening is preferably performed by etchingthe metal foil. The etching process may be performed by using, forexample, a direct current electrolysis method or an alternating currentelectrolysis method.

(Fiber Structure)

A fiber structure is used as the raw material of the separator.

The fiber structure is not particularly limited as long as it is porous.Examples of the fiber structure include a woven fabric, a knit, and anon-woven fabric that contain fibers.

In order to prevent the occurrence of wrinkles caused by the conductivepolymer dispersion liquid that contains water as the dispersion mediumbeing attached to the fiber structure, the fiber structure contains asynthetic fiber in an amount of 50 mass % or more, or contains acellulose fiber and a paper strengthening agent. As a result of theoccurrence of wrinkles in the fiber structure being suppressed, theconductive polymer dispersion liquid (hereinafter referred to as “firstdispersion liquid”) is uniformly attached to the fiber structure, andthe resulting separator has a uniform thickness. For this reason, in theelectrolytic capacitor, the likelihood of the withstand voltage andinter-electrode resistance varying from place to place is suppressed.

In the fiber structure (hereinafter referred to as “first fiberstructure”) that contains a synthetic fiber in an amount of 50 mass % ormore, the amount of the synthetic fiber may be 70 mass % or more of thefiber structure. The type of synthetic fiber is not particularlylimited. From the viewpoint of strength and unlikeliness of swellingwith water, the synthetic fiber may contain at least one selected fromthe group consisting of a nylon fiber, an aramid fiber, an acrylicfiber, and a polyester fiber.

The first fiber structure may further contain cellulose from theviewpoint of having good affinity for a first dispersion liquid, anelectrolytic solution that is also added where necessary, and a secondconductive polymer dispersion liquid (hereinafter referred to as “seconddispersion liquid”), which will be described later. Considering theability of holding the electrolytic solution, the amount of cellulosemay be 10 mass % or more of the fiber structure. The amount of cellulosemay be less than 50 mass %, 30 mass % or less, or 20 mass % or less.

In the fiber structure (hereinafter referred to as “second fiberstructure”) that contains a cellulose fiber and a paper strengtheningagent, the type of paper strengthening agent is not particularlylimited, and a wet paper strengthening agent and/or a dry paperstrengthening agent may be used. These may be used alone or incombination. As the wet paper strengthening agent, for example, at leastone selected from the group consisting of a urea formaldehyde resin, amelamine formaldehyde resin, a polyamide polyamine epichlorohydrin, anda polyvinylamine can be used. As the dry paper strengthening agent, forexample, at least one selected from the group consisting of apolyacrylamide, a polyvinyl alcohol, a starch, and a carboxymethylcellulose can be used.

The paper strengthening agent may be added to the raw material of thesecond fiber structure (for example, a slurry that contains a cellulosefiber), or applied to the second fiber structure by spraying or thelike.

In the case where the paper strengthening agent is added, the secondfiber structure may contain cellulose in an amount of 40 mass % or moreor 70 mass % or more. The second fiber structure may further contain asynthetic fiber. The amount of the synthetic fiber may be, for example,10 mass % or more and 60 mass % or less of the second fiber structure.

Each fiber structure has a density of 0.2 g/cm³ or more and less than 045 g/cm³. Even when a fiber structure that has a small density is used,by containing a synthetic fiber in an amount of 50 mass % or more, orcontaining a cellulose fiber and a paper strengthening agent, swellingof the fiber structure with the water dispersion medium is suppressed.The density of the fiber structure (including the paper strengtheningagent) may be, for example, 0.25 g/cm³ or more and 0.40 g/cm³ or less.

The thickness of each fiber structure is not particularly limited. Thethickness of each fiber structure may be, for example, 20 μm or more and100 μm or less, and is preferably 30 μm or more and 60 μm or less. Withthis configuration, in the resulting electrolytic capacitor, the shortcircuiting is likely to be suppressed, and the effect of reducing theESR can be further improved.

(2) Step of Preparing a First Dispersion Liquid (S2)

A first dispersion liquid that contains a first conductive polymercomponent (hereinafter referred to as “first polymer component”) and afirst dispersion medium is prepared.

(First Dispersion Liquid)

The first dispersion liquid contains a first polymer component and afirst dispersion medium.

The first polymer component contains a conductive polymer. Examples ofthe conductive polymer include polypyrrole, polythiophene, polyfuran,polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene,polyacene, polythiophene vinylene, and the like. These may be used aloneor in a combination of two or more, or a copolymer that contains two ormore types of monomers may be used.

In the specification of the present application, each of polypyrrole,polythiophene, polyfuran, polyaniline, and the like means a polymer inwhich polypyrrole, polythiophene, polyfuran, polyaniline, or the like isused as the basic backbone. Accordingly, polypyrrole, polythiophene,polyfuran, polyaniline, and the like may also include derivativesthereof. For example, polythiophene includespoly(3,4-ethylenedioxythiophene), and the like.

The first polymer component may further contain a dopant. The dopant maybe a polyanion. Specific examples of the polyanion include polyvinylsulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid,polyacrylic sulfonic acid, polymethacryl sulfonic acid,poly(2-acrylamide-2-methylpropane sulfonic acid), polyisoprene sulfonicacid, polyacrylic acid, and the like. These may be used alone or in acombination of two or more. Also, they may be a polymer that containssole monomers, or a copolymer that contains two or more types ofmonomers. Among these, it is preferable to use a polystyrene sulfonicacid-derived polyanion.

The weight-average molecular weight of the polyanion (hereinafterreferred to as “first polyanion”) contained in the first polymercomponent is not particularly limited. The weight-average molecularweight of the first polyanion may be, for example, 1,000 or more and200,000 or less. The first polymer component that contains the firstpolyanion is likely to be homogeneously dispersed in the firstdispersion medium and attached to the separator. Also, theweight-average molecular weight of the first polyanion may be 1,000 ormore and 70,000 or less. Even when a large amount of the first polyanionis contained, an excessive increase in the viscosity of the firstdispersion liquid is suppressed, and the amount of the first polymercomponent that is attached to the separator is likely to increase.

The first polymer component is dispersed in the first dispersion mediumin the form of, for example, particles. The average particle size of theparticles of the first polymer component is not particularly limited,and can be adjusted as appropriate according to the polymerizationconditions, the dispersion conditions, and the like. For example, theaverage particle size of the particles of the first polymer componentmay be 0.01 μm or more and 0.5 μm or less. As used herein, the term“average particle size” refers to the median diameter of thevolume-based particle size distribution measured by using a particlesize measurement apparatus that uses a dynamic light scattering method.

The first dispersion medium contains water. The first dispersion mediummay contain a non-aqueous solvent. The term “non-aqueous solvent” is ageneral term for a liquid excluding water, and includes an organicsolvent and an ionic liquid. Water may account for 50 mass % or more, 70mass % or more, or 90 mass % or more of the first dispersion medium. Asthe non-aqueous solvent that is used together with water, a polarsolvent (a protic solvent and/or an aprotic solvent) may be used.

Examples of the protic solvent include: alcohols such as methanol,ethanol, propanol, butanol, ethylene glycol (EG), propylene glycol,polyethylene glycol (PEG), diethylene glycol monobutyl ether, glycerin,1-propanol, butanol, polyglycerin, sorbitol, mannitol, andpentaerythritol; formaldehyde; and the like. Examples of the aproticsolvent include: amides such as N-methylacetamide,N,N-dimethylformamide, and N-methyl-2-pyrrolidone; esters such as methylacetate, γ-butyrolactone (γBL); ketones such as methyl ethyl ketone;ethers such as 1,4-dioxane; sulfur-containing compounds such as dimethylsulfoxide and sulfolane (SL); carbonate compounds such as propylenecarbonate; and the like.

In the case where the first dispersion medium contains an alcohol asdescribed above (in particular, a polyhydric alcohol or a sugaralcohol), electric conductivity and the impregnation ability into theseparator are likely to increase. On the other hand, polyhydric alcoholsand sugar alcohols tend to swell cellulose. The fiber structureaccording to the present embodiment is unlikely to swell with the firstdispersion medium that contains an alcohol as described above, and thusthe occurrence of wrinkles is suppressed.

The first dispersion liquid can be obtained by using, for example, amethod in which the particles of the first polymer component aredispersed in the first dispersion medium, a method in which precursormonomers of the first polymer component are polymerized in the firstdispersion medium to produce particles of the first polymer component inthe first dispersion medium, or the like.

The amount of the first polymer component is not particularly limited.The first polymer component may be contained in the first dispersionliquid in an amount of 1 mass % or more and 15 mass % or less. When theamount of the first polymer component is within this range, a sufficientamount of the first polymer component can be attached to the fiberstructure. From the viewpoint of further increasing the amount of thefirst polymer component that is attached to the fiber structure, theamount of the first polymer component may be 3 mass % or more.

The viscosity of the first dispersion liquid is not particularlylimited. The first dispersion liquid may have a viscosity of 10 mPa·s ormore, the viscosity being measured at room temperature (20° C.) by usinga vibration viscometer (for example, VM-100A available from SekonicCorporation). Also, the viscosity of the first dispersion liquidmeasured under the conditions described above may be 100 mPa·s or moreand 200 mPa·s or less. The first dispersion liquid that has a viscositywithin this range is particularly suitable for use in a coating method.

(3) Step of Producing a Separator (Step of Forming a Polymer Layer (S3))

A separator that contains the first polymer component is produced byapplying the first dispersion liquid to the fiber structure and thenremoving at least a portion of the first dispersion medium. By applyingthe first dispersion liquid to the fiber structure that is the rawmaterial of the separator prior to producing the capacitor element, asufficient amount of the first polymer component can be attached to thefiber structure. The first polymer component is attached to the surfacesof the fibers that constitute the fiber structure.

The method for applying the first dispersion liquid is not particularlylimited. The fiber structure may be impregnated with the firstdispersion liquid, or the first dispersion liquid may be applied to thefiber structure by using a coating method.

The coating method is a technique for applying a liquid substance to atarget object by using a coater. As the coater, for example, any ofknown apparatuses including a gravure coater, a knife coater, a commacoater, a roll coater, a die coater, and a lip coater may be used.

The amount of the first dispersion liquid applied to the fiber structureis not particularly limited. For example, the amount of the firstdispersion liquid applied to the fiber structure may be set asappropriate such that the first polymer component is attached to thefiber structure in an amount of 0.02 mg/cm² or more.

The coating process that uses the first dispersion liquid may beperformed on one or both sides of the fiber structure. The coatingprocess that uses the first dispersion liquid may be performed on thesame side of the fiber structure a plurality of times. With thisconfiguration, the amount of the first polymer component that isattached to the fiber structure can be increased. In this case, thecoating process may be performed continuously a plurality of times,followed by a drying process. Alternatively, the drying process may beperformed each time the coating process is performed.

From the viewpoint of mass production, the step of producing a separatormay be performed on a long fiber structure. In the case where thecoating process is performed on both sides of a fiber structure that isa long strip, first, the coating process is performed on one side,followed by a drying process, and then, the fiber structure is spirallywound into a roll. After that, the coating process may be performed onthe other side by using the same coater or a different coater while thefiber structure is dispensed by unwinding from the roll such that thefiber structure is flipped.

From the viewpoint of increasing the amount of the conductive polymercomponent, the first polymer component may also be attached to aconstituent member other than the separator included in the capacitorelement. Particularly in the case where the first polymer component isattached to the cathode foil and the separator, it is possible to causethe capacitor element to hold a sufficient amount of the conductivepolymer component without compromising the self-repairing ability of theanode foil. In the case where the first polymer component is attached tothe anode foil and the separator, the adhesion between the dielectriclayer formed on the anode foil and the first polymer component isimproved, and thus the ESR is more likely to be reduced. The method forattaching the first polymer component to a constituent member other thanthe separator is not particularly limited, and an impregnation method ora coating method may be used.

The first dispersion medium may be removed by using, for example, adrying process such as heat drying or vacuum drying. The drying processis not particularly limited, and may be selected as appropriateaccording to the type of the first dispersion medium, the amount of thefirst dispersion liquid applied, and the like. At this time, the dryingprocess may be performed such that the first dispersion medium is notcompletely removed. For example, the drying process may be performedsuch that the amount of the first dispersion medium contained in thefirst dispersion liquid immediately after the coating process becomes 0mass % or more and 10 mass % or less.

In the case where the capacitor element is impregnated with a seconddispersion liquid and/or an electrolytic solution in a step that isperformed later, when the first polymer component is attached to theseparator together with the first dispersion medium, the seconddispersion liquid and/or the electrolytic solution is induced by thefirst dispersion medium and easily permeate into the pores of theseparator. Accordingly, the anode foil and the cathode foil are morelikely to come into contact with the second dispersion liquid and/or theelectrolytic solution, as a result of which, an improvement in theself-repairing ability of the anode foil and an increase in theelectrostatic capacitance can be expected. Furthermore, cracking isunlikely to occur in the first polymer component even when the longseparator to which the first polymer component has been attached isspirally wound into a roll.

(4) Step of Cutting the Separator (S4)

The long separator to which the first polymer component has beenattached is cut prior to the step of producing a capacitor element. Longconstituent members other than the separator may also be cut in thisstep, for example.

(5) Step of Producing a Capacitor Element (S5)

The anode foil and the cathode foil are stacked such that the separatoris interposed between the anode foil and the cathode foil. The stackedbody including the anode foil, the separator, and the cathode foil maybe spirally wound. In this case, the end portion of the outermost layerof the cathode foil is fixed by using a fixing tape. In the case wherethe cutting step was performed, in order to form a dielectric layer onthe cut surface of the anode foil, a chemical formation treatment (achemical reformation treatment) may be further performed on thecapacitor element

(6) Step of Impregnating the Capacitor Element with a Second DispersionLiquid (S6)

Where necessary, the capacitor element may be impregnated with a seconddispersion liquid that contains a second conductive polymer component(hereinafter referred to as “second polymer component”) and a seconddispersion medium. The method for impregnating the capacitor elementwith the second dispersion liquid is not particularly limited. After thecapacitor element has been impregnated with the second dispersionliquid, a drying process may be performed to remove at least a portionof the second dispersion medium.

By drying the capacitor element after it has been impregnated with thesecond dispersion liquid, the second polymer component can be attachedto the inside of the capacitor element. By incorporating the secondpolymer component, the electrostatic capacitance further increases, anda reduction in the ESR can be expected. The second polymer component isattached primarily to the inside of pits or the pores of the constituentmembers of the capacitor element

(Second Dispersion Liquid)

The second dispersion liquid contains, for example, a second polymercomponent and a second dispersion medium.

As the second dispersion medium, the same compounds as those describedfor the first dispersion medium can be used.

The second polymer component is not particularly limited, and maycontain a conductive polymer and a dopant that are the same as thosecontained in the first polymer component. The second polymer componentmay contain, as the dopant, a polyanion (hereinafter referred to as“second polyanion”). In this case, the weight-average molecular weightof the second polyanion is preferably higher than the weight-averagemolecular weight of the first polyanion contained in the first polymercomponent. With this configuration, the electric conductivity of thesecond polymer component is higher, and it is therefore possible toeffectively reduce the ESR by using only a small amount. Furthermore,the viscosity of the second dispersion liquid is also reduced, and thusthe impregnation ability into the capacitor element increases.

The weight-average molecular weight of the second polyanion may be, forexample, 1,000 or more and 200,000 or less, or 75,000 or more and150,000 or less.

In the second dispersion liquid, the amount of the second polymercomponent may be smaller than the amount of the first polymer componentcontained in the first dispersion liquid. Specifically, the amount ofthe second polymer component contained in the second dispersion liquidis preferably 0.5 mass % or more and less than 3 mass %. The viscosityof the second dispersion liquid measured at room temperature (20° C.) byusing a vibration viscometer is preferably lower than the viscosity ofthe first dispersion liquid measured under the same conditions. Theviscosity of the second dispersion liquid measured at room temperature(20° C.) by using a vibration viscometer is preferably less than 100mPa·s.

(7) Step of Impregnating the Capacitor Element with an ElectrolyticSolution (S7)

Where necessary, the capacitor element may be impregnated with anelectrolytic solution. The capacitor element may be impregnated with anelectrolytic solution, without performing the step of impregnating itwith the second dispersion liquid. Alternatively, the capacitor elementmay be impregnated with an electrolytic solution after the capacitorelement has been impregnated with the second dispersion liquid. Byincorporating the electrolytic solution, the self-repairing ability ofthe dielectric layer is likely to be improved. Also, the electrolyticsolution functions as a substantial cathode material, and thus theeffect of increasing the electrostatic capacitance can be expected. Themethod for impregnating the capacitor element with the electrolyticsolution is not particularly limited.

(Electrolytic Solution)

The electrolytic solution contains a solvent.

Examples of the solvent include a sulfone compound, a lactone compound,a carbonate compound, a polyhydric alcohol, and the like. Examples ofthe sulfone compound include sulfolane, dimethyl sulfoxide, diethylsulfoxide, and the like. Examples of the lactone compound includeγ-butyrolactone, γ-valerolactone, and the like. Examples of thecarbonate compound include dimethylcarbonate (DMC), diethylcarbonate(DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylenecarbonate (PC), fluoroethylene carbonate (FEC), and the like. Examplesof the polyhydric alcohol include: glycol compounds such as ethyleneglycol (EG), diethylene glycol, triethylene glycol, propylene glycol,and polyethylene glycol (PEG); glycerin; and the like. These may be usedalone or in a combination of two or more.

In particular, the solvent may contain a compound that has two or morehydroxy groups. An example of the compound that has two or more hydroxygroups is a polyhydric alcohol. The amount of the compound that has twoor more hydroxy groups may be 50 mass % or more, 60 mass % or more, or70 mass % or more of the total amount of the solvent

The electrolytic solution may further contain an acid component. In thecase where the first polymer component or the second polymer componentcontains a dopant, the acid component contained in the electrolyticsolution suppresses the dedoping phenomenon of the dopant and stabilizesthe conductivity of the polymer component. Also, even when the dopant isdedoped from the polymer component, the site where dedoping occurred isdoped again with the acid component of the electrolytic solution, andthus the ESR is likely to be maintained at a low level.

It is desirable that the acid component contained in the electrolyticsolution easily dissociates in the electrolytic solution and producesanions that can easily move in the solvent, without excessivelyincreasing the viscosity of the electrolytic solution. Examples of theacid component include aliphatic sulfonic acids with 1 to 30 carbonatoms and aromatic sulfonic acids with 6 to 30 carbon atoms. Among thealiphatic sulfonic acids, a saturated aliphatic monosulfonic acid (forexample, hexane sulfonic acid) is preferable. Among the aromaticsulfonic acids, an aromatic sulfonic acid that has, in addition to asulfo group, a hydroxy group or a carboxy group is preferable.Specifically, oxy aromatic sulfonic acids (for example,phenol-2-sulfonic acid) and sulfo aromatic carboxylic acids (forexample, p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylicacid) are preferable.

As another acid component, a carboxylic acid may be used. The carboxylicacid preferably includes an aromatic carboxylic acid (aromaticdicarboxylic acid) that has two or more carboxyl groups. Examples of thearomatic carboxylic acid include phthalic acid (ortho form), isophthalicacid (meta form), terephthalic acid (para form), maleic acid, benzoicacid, salicylic acid, trimellitic acid, and pyromellitic acid. Amongthese, the aromatic dicarboxylic acid is more preferably phthalic acid(ortho form) or maleic acid. The carboxyl groups in the aromaticdicarboxylic acid are stable, and thus do not easily cause a sidereaction to proceed. Accordingly, the effect of stabilizing theconductive polymer is exhibited for a long period of time, and it istherefore advantageous for extending the service life of theelectrolytic capacitor. Also, the carboxylic acid may be an aliphaticcarboxylic acid such as adipic acid.

The acid component may contain a composite compound that contains anorganic acid and an inorganic acid, from the viewpoint of thermalstability. Examples of the composite compound that contains an organicacid and an inorganic acid include borodisalicylic acid, borodioxalicacid, borodiglycollic acid, and the like that have high heat resistance.

The acid component may contain an inorganic acid such as boric acid,phosphoric acid, phosphorous acid, hypophosphorous acid, or phosphonicacid.

From the viewpoint of enhancing the effect of suppressing the dedopingphenomenon, the concentration of the acid component may be set to 5 mass% or more and 50 mass % or less, or 15 mass % or more and 35 mass % orless.

The electrolytic solution may contain a basic component together withthe acid component. By incorporating the basic component, at least aportion of the acid component is neutralized. Accordingly, the corrosionof electrodes due to the acid component can be suppressed whileincreasing the concentration of the acid component. From the viewpointof effectively suppressing dedoping, the amount of the acid component ispreferably in excess of that of the basic component in terms ofequivalence ratio. For example, the equivalence ratio of the acidcomponent relative to the basic component may be 1 or more and 30 orless. The concentration of the basic component contained in theelectrolytic solution may be 0.1 mass % or more and 20 mass % or less,or 3 mass % or more and 10 mass % or less.

The basic component is not particularly limited. Examples of the basiccomponent include ammonia, a primary amine, a secondary amine, atertiary amine, a quaternary ammonium compound, an amidinium compound,and the like. Each amine may be an aliphatic amine, an aromatic amine, aheterocyclicamine, and the like.

The electrolytic solution preferably has a pH of 4 or less, morepreferably 3.8 or less, and even more preferably 3.6 or less. By settingthe pH of the electrolytic solution to 4 or less, the deterioration ofthe polymer component is further suppressed. The pH is preferably 2.0 ormore.

(8) Step of Sealing the Capacitor Element (S8)

The produced capacitor element is housed in a bottomed case. As thematerial of the bottomed case, a metal such as aluminum, stainlesssteel, copper, iron, or brass, or an alloy thereof can be used. Afterthat, the vicinity of the opening end of the bottomed case ishorizontally squeezed, and the opening end is curled and crimped onto asealing member, and the capacitor element is thereby sealed. Finally, acover plate is placed on the curled portion, and an electrolyticcapacitor is obtained. Then, the electrolytic capacitor may be subjectedto an aging process while applying the rated voltage.

[Electrolytic Capacitor]

The electrolytic capacitor according to the present embodiment includesan anode foil that includes a dielectric layer, a cathode foil, and aseparator that is interposed between the anode foil and the cathodefoil. The separator contains a fiber structure and a first polymercomponent that is attached to the fiber structure. The fiber structurecontains a synthetic fiber in an amount of 50 mass % or more, and has adensity of 0.2 g/cm³ or more and less than 45 g/cm³.

Another electrolytic capacitor according to the present embodimentincludes an anode foil that includes a dielectric layer, a cathode foil,and a separator that is interposed between the anode foil and thecathode foil. The separator contains a fiber structure and a firstpolymer component that is attached to the fiber structure. The fiberstructure contains a cellulose fiber in an amount of 40 mass % or moreand a paper strengthening agent, and has a density of 0.2 g/cm³ or moreand less than 0.45 g/cm³.

Hereinafter, constituent members other than the separator of thecapacitor element and other constituent materials will be described.

(First Polymer Component)

The first polymer component is attached to the separator.

Hereinafter, a conductive polymer component that is attached to theseparator and contains a first polymer component may also be referred toas “first polymer layer”.

The mass of the first polymer layer per unit area of the separator isnot particularly limited, and may be set as appropriate where necessary.According to the present embodiment, the first polymer layer can beattached to the separator in an amount of 0.02 mg/cm² or more. The massof the first polymer layer may be 0.1 mg/cm² or less per unit area.

The mass of the first polymer layer can be calculated from thedifference in the mass of the fiber structure between before and afterthe application of the first dispersion liquid. Alternatively, the massof the first polymer layer may be calculated by analyzing the separatorby using a thermogravimetric analysis method (TGA method). With the TGAmethod, for example, thermal change when the temperature of a specimenis increased at a fixed speed, the amount of reduction in the specimen,and the like are measured. The mass of the first polymer layer attachedto the separator can be calculated based on the measured values.

The first polymer component is attached to the surfaces of the fibersthat constitute the separator. For this reason, the first polymer layermay also be formed on the outer surface of the separator.

A higher effect of reducing the ESR can be obtained as the electricconductivity of the first polymer layer is higher. The electricconductivity of the first polymer layer may be, for example, 30 S/cm ormore, or 300 S/cm or more. The electric conductivity of the firstpolymer layer is likely to be higher as the molecular weight of theconductive polymer contained is higher. The viscosity of the firstdispersion liquid is likely to increase as the molecular weight of theconductive polymer increases. For this reason, the molecular weight ofthe conductive polymer may be set such that the viscosity of the firstdispersion liquid does not increase excessively.

In the case where a first dispersion liquid that has a first polymercomponent concentration of 3 mass % or more is used, the electricconductivity of the first polymer layer is preferably set to, forexample, 170 S/cm or less. With this configuration, an excessiveincrease in the viscosity of the first dispersion liquid is suppressed.In this case, the electric conductivity of the first polymer layer maybe 150 S/cm or less or 120 S/cm or less. The electric conductivity ofthe first polymer layer is the electric conductivity of a film obtainedby applying the first dispersion liquid to a substrate and then removingthe first dispersion medium. The electric conductivity of the film ismeasured in accordance with the testing method with a four-point probearray that conforms to JIS K 7194: 1994.

(Second Polymer Component)

In the capacitor element, the second polymer component described abovemay be provided. By incorporating the second polymer component, theelectrostatic capacitance further increases, and a further reduction inthe ESR can be expected. The second polymer component may be providedby, for example, impregnating the capacitor element with the seconddispersion liquid described above.

Hereinafter, a conductive polymer component that contains a secondpolymer component and is different from the first polymer layer may bereferred to as “second polymer layer”.

The second polymer layer may be attached to the inside of pits or thepores on the surface of the constituent member of the capacitor element.The second polymer layer may be attached so as to cover a portion of thefirst polymer layer attached to the outer surface of the separator.Furthermore, the second polymer layer may be provided in the gapsbetween the fibers that constitute the separator to which the firstpolymer layer has been attached.

The second polymer layer is provided in the capacitor element in anamount of, for example, 0.01 mg/cm² or more and less than 1 mg/cm². Theamount of the second polymer layer provided is calculated in the samemanner as that of the first polymer component is calculated. In the casewhere the separator is analyzed by using the TGA method, the amount ofthe second polymer layer attached to the separator can be obtained bysubtracting the amount of the first polymer layer attached to theseparator from the calculated amount of the two polymer layers attachedto the separator. The total of the amount of the second polymer layerattached to the separator and the amount of the second polymer layerattached to other constituent members (for example, the anode foiland/or the cathode foil) calculated by using the TGA method is theamount of the second polymer layer provided in the capacitor element. Bydividing the total amount of the second polymer layer provided in thecapacitor element by the total value of the area of one of the mainsurfaces of each constituent member, the mass of the second polymerlayer per unit area is obtained.

According to the present embodiment, when the separator is viewed fromthe normal direction of the main surface of the separator, for example,50% or more of the area of the main surface is covered by a polymerlayer. The polymer layer may include the first polymer layer and thesecond polymer layer. The area coverage covered by the polymer layer maybe 60% or more, and is preferably 90% or more. The polymer layer may becontinuous or discontinuous on the surface of the separator. The polymerlayer that has such a high coverage is likely to be formed when thefirst dispersion liquid is applied by using a coating method. The areacoverage is calculated by using the separator for use in theelectrolytic capacitor that has been cut into a predetermined size. Thearea coverage may be calculated by binarizing an image obtained bycapturing the main surface of the constituent member.

The area coverage covered by the polymer layer can be regarded as thearea coverage covered by the first polymer layer. The area coverage ofthe surface of the separator covered by the second polymer layer issmaller than the area coverage covered by the first polymer layer. Thearea coverage covered by the second polymer layer is, for example, 90%or less or 60% or less.

The mass (density) of the first polymer layer attached to the separatorper unit area is preferably higher than the mass (density) of the secondpolymer layer attached to the same per unit area. The ratio of thedensity of the first polymer layer relative to the density of the secondpolymer layer is obtained by observing a cross-section of the separatorby using a scanning electron microscope (SEM) or the like. The ratio ofthe density of the first polymer layer relative to the density of thesecond polymer layer is obtained by dividing the area of the firstpolymer layer that is in contact with the separator by the area of apolymer layer other than the first polymer layer. The densities of thepolymer layers are calculated by observing the same observation field ofthe same separator. Ordinarily, an interface can be observed between thefirst polymer layer and the second polymer layer. Accordingly, it ispossible to distinguish the first polymer layer and the second polymerlayer from each other. The amount, the area coverage, the density, andthe like of the first polymer layer attached are calculated excluding aregion of the separator on which the first polymer layer is notintentionally formed. It is desirable that the observation field has anarea of 100 μm² or more.

(Anode Foil)

The anode foil is a metal foil that contains at least one of valvemetals including titanium, tantalum, aluminum, and niobium. The anodefoil may contain the valve metal in the form of an alloy that containsthe valve metal, a compound that includes the valve metal, or the like.The thickness of the anode foil is not particularly limited, and is, forexample, 15 μm or more and 300 μm or less. The thickness is the averagevalue of measured values obtained at arbitrarily selected five points(the same applies hereinafter). The surface of the anode foil may beroughened by etching or the like.

A dielectric layer is formed on the surface of the anode foil. Thedielectric layer is formed by, for example, subjecting the anode foil toa chemical formation treatment. In this case, the dielectric layer maycontain an oxide of the valve metal. The dielectric layer is not limitedto the configuration described above as long as it functions as adielectric. It is desirable that the dielectric layer is also formed oneach end surface of the anode foil.

(Cathode Foil)

The cathode foil is not particularly limited as long as it functions asa cathode. The cathode foil may be a metal foil. Type of metal is notparticularly limited, and may be a valve metal or an alloy that containsa valve metal, as with the anode foil. The thickness of the cathode foilis not particularly limited, and may be, for example, 15 μm or more and300 μm or less. The surface of the cathode foil may be subjected tosurface roughening or chemical formation treatment where necessary.

In the case where the metal foil contains a valve metal, the metal foilmay include a conductive coating layer that contains at least oneselected from the group consisting of carbon and metals that have anionization tendency lower than the valve metal. With this configuration,the acid resistance is likely to be improved. In the case where themetal foil contains aluminum, the coating layer may contain at least oneselected from the group consisting of carbon, nickel, titanium,tantalum, and zirconium. Among these, from the viewpoint of cost andresistance, the coating layer may contain nickel and/or titanium.

The thickness of the coating layer is not particularly limited. Thethickness of the coating layer may be, for example, 5 nm or more and 200nm or less, or 10 nm or more and 200 nm or less. The thickness of thecoating layer may be measured by using, for example, an X-rayphotoelectron spectroscopy method (XPS method). The coating layer can beformed by, for example, vapor depositing or sputtering any of the metalsdescribed above on a metal foil. Alternatively, the coating layer can beformed by vapor depositing a conductive carbon material on a metal foil,or applying a carbon paste that contains a conductive carbon material toa metal foil. Examples of the conductive carbon material includegraphite, hard carbon, soft carbon, carbon black, and the like.

B. Second Embodiment [Conductive Polymer Dispersion Liquid]

The conductive polymer dispersion liquid (hereinafter referred to as“first dispersion liquid”) contains a conductive polymer component(hereinafter referred to as “first polymer component”) and a dispersionmedium (hereinafter referred to as “first dispersion medium”).

The first polymer component is contained in the first dispersion liquidin an amount of 3 mass % or more and 15 mass % or less. When the amountof the first polymer component is within this range, the viscosity ofthe first dispersion liquid is likely to be high. For this reason, asufficient amount of the first polymer component can be applied to theconstituent member. The amount of the first polymer component may be 10mass % or less, or 8 mass % or less

The viscosity of the first dispersion liquid measured at roomtemperature (20° C.) by using a vibration viscometer (for example,VM-100A available from Sekonic Corporation) is 100 mPa·s or more. Also,the viscosity of the first dispersion liquid measured under the sameconditions may be 200 mPa·s or less or 180 mPa·s or less. The firstdispersion liquid that has a viscosity within this range is particularlysuitable for use in a coating method.

The first polymer component contains a conductive polymer. As theconductive polymer, the same as described in the first embodiment can beused.

The first polymer component may further contain a dopant. As the dopant,the same as described in the first embodiment can be used.

The first polymer component is dispersed in the first dispersion mediumin the form of, for example, particles. The average particle size of theparticles of the first polymer component is not particularly limited,and can be adjusted as appropriate according to the polymerizationconditions, the dispersion conditions, and the like.. For example, theaverage particle size of the particles of the first polymer componentmay be 0.01 μm or more and 0.5 μm or less. As used herein, the term“average particle size” refers to the median diameter of thevolume-based particle size distribution measured by using a particlesize measurement apparatus that uses a dynamic light scattering method.

The first dispersion medium is not particularly limited, and may bewater, a non-aqueous solvent, or a mixture thereof. The non-aqueoussolvent is a general term for a liquid excluding water, and includes anorganic solvent and an ionic liquid. Among these, the first dispersionmedium may be water from the viewpoint of ease of handling and thedispersibility of the conductive polymer component. Water may accountfor 50 mass % or more, 70 mass % or more, or 90 mass % or more of thefirst dispersion medium. As the non-aqueous solvent that can be usedtogether with water, a polar solvent (a protic solvent and/or an aproticsolvent) may be used.

As the protic solvent, the same as described in the first embodiment canbe used.

The first dispersion liquid can be obtained by using, for example, amethod in which the particles of the first polymer component aredispersed in the first dispersion medium, a method in which precursormonomers of the first polymer component are polymerized in the firstdispersion medium to produce particles of the first polymer component inthe first dispersion medium, or the like.

The first dispersion liquid is suitable for applying the first polymercomponent to the constituent member of the capacitor element by using acoating method. The first dispersion liquid may be applied to theconstituent member of the capacitor element by using an immersionmethod.

By applying the first dispersion liquid to the constituent member priorto producing the capacitor element, it is possible to uniformly attach asufficient amount of the first polymer component to the constituentmember. In the case where the constituent member is porous or has pitson the surface thereof, a portion of the first dispersion liquid maypermeate into the pores of the constituent member.

When the first dispersion liquid is dried, and at least a portion of thefirst dispersion medium is removed after the first dispersion liquid hasbeen applied, a conductive polymer layer (hereinafter referred to as“first polymer layer”) that contains the first polymer component isformed so as to cover at least a portion of the surface of theconstituent member. In other words, at least a portion of the firstpolymer layer is provided on the outermost surface of the constituentmember.

[Method for Producing Electrolytic Capacitor]

The electrolytic capacitor according to the present embodiment can beproduced by using a method including the steps of: preparing asheet-like member that constitute a capacitor element; preparing a firstdispersion liquid as described above; forming a first polymer layer thatcontains a first polymer component by applying the first conductivepolymer dispersion liquid to the sheet-like member by using a coatingmethod and then removing at least a portion of the first dispersionmedium; and producing a capacitor element by using the sheet-like memberon which the first polymer layer has been formed.

FIG. 2 is a flowchart illustrating an example of a method for producingan electrolytic capacitor according to a second embodiment of thepresent invention.

Hereinafter, each of the steps included in the example of the method forproducing an electrolytic capacitor according to the present embodimentwill be described.

(1) Step of Preparing Constituent Members (S1)

The sheet-like constituent members that are members to which the firstdispersion liquid is to be applied may be an anode foil, a cathode foil,a separator, and the like.

The anode foil and the cathode foil are prepared in the same manner asin the first embodiment.

As the raw material of the separator, a known fiber structure may beprepared, or a fiber structure that is the same as that of the firstembodiment may be prepared.

(2) Step of Preparing a First Dispersion Liquid (S2)

The above-described first dispersion liquid that contains a firstpolymer component and a first dispersion medium is prepared.

(3) Step of Forming a Polymer Layer (S3)

The first polymer layer that contains the first polymer component isformed by applying the first dispersion liquid to at least one selectedfrom the group consisting of the anode foil, the cathode foil, and theseparator by using a coating method, and then removing at least aportion of the first dispersion medium. As the coating method, the sameas described in the first embodiment can be used. In the presentembodiment, the first dispersion liquid is applied to the constituentmember by using any one of known coaters listed.

From the viewpoint of increasing the amount of the first polymercomponent, it is desirable that the first dispersion liquid is appliedto all of the constituent members.

In the case where an electrolytic solution is used together, it isdesirable that the first dispersion liquid is applied to at least one ortwo constituent members. The reason is that it is possible to cause thecapacitor element to hold a sufficient amount of the first polymercomponent without impeding the permeation of the electrolytic solutioninto other constituent members. Particularly in the case where the firstpolymer layer is formed on the cathode foil and/or the separator, it ispossible to cause the capacitor element to hold a sufficient amount ofthe first polymer component without compromising the self-repairingability of the anode foil. In the case where the first polymer layer isformed on the anode foil, the adhesion between the dielectric layerformed on the surface of the anode foil and the first polymer componentis improved, and thus the ESR is more likely to be reduced.

The amount of the first dispersion liquid applied to each constituentmember is not particularly limited. For example, the amount of the firstdispersion liquid applied to the constituent member may be set asappropriate such that the first polymer layer is formed on theconstituent member in an amount of 0.04 mg/cm² or more. In particular,the amount of the first dispersion liquid applied to the constituentmember may be set as appropriate such that the first polymer layer isformed on the separator in an amount of 0.04 mg/cm² or more. The amountof the first dispersion liquid applied to each of the anode foil and thecathode foil may be set as appropriate such that the first polymer layeris formed in an amount of 0.1 mg/cm² or more. The amount of the firstdispersion liquid applied is the total mass of the first polymercomponent that has been attached to the surface of each constituentmember and the pores and pits of the constituent member per unit area.

The coating process that uses the first dispersion liquid may beperformed on only one side or both sides of at least one selected fromthe group consisting of the anode foil, the cathode foil, and theseparator. The coating process that uses the first dispersion liquid maybe performed on the same side of the constituent member a plurality oftimes. With this configuration, the amount of the first polymer layerformed can be increased. In this case, the coating process may beperformed continuously a plurality of times, followed by a dryingprocess. Alternatively, the drying process may be performed each timethe coating process is performed.

From the viewpoint of mass production, the step of forming a firstpolymer layer may be performed on a long constituent member. In the casewhere the coating process is performed on both sides of the constituentmember that is a long strip, first, the coating process is performed onone side, followed by a drying process, and then, the constituent memberis spirally wound into a roll. After that, that, the coating process maybe performed on the other side by using the same coater or a differentcoater while the constituent member is dispensed by unwinding from theroll such that the constituent member is flipped.

In the case where a cutting step, which will be described later, isperformed after the first polymer layer has been formed, it is desirablethat the coating process is performed such that the first polymer layeris not formed on a cutting line along which the constituent member is tobe cut. With this configuration, the likelihood of the first polymerlayer being damaged or separated by being cut is suppressed.Particularly when the first polymer layer is formed on the anode foil,it is desirable that the coating process is performed such that thefirst polymer layer is not formed on a cutting line along which theanode foil is to be cut. With this configuration, it is possible toavoid the first polymer component attaching to the cut surface. When theanode foil is cut, the cut surface may include a portion that does notinclude the dielectric layer. Accordingly, there may be a case where achemical formation treatment is performed again after the cutting step.In this case as well, the dielectric layer is likely to be formeduniformly on the cut surface.

The first dispersion medium may be removed in the same manner as in thefirst embodiment.

In the case where the capacitor element is impregnated with a secondconductive polymer dispersion liquid (hereinafter referred to as “seconddispersion liquid”) and/or an electrolytic solution in a step performedlater, when the first polymer layer contains the first dispersionmedium, the second dispersion liquid and/or the electrolytic solution isinduced by the first dispersion medium and easily permeates into thesurfaces, pores, and etching pits of the dielectric layers formed on theanode foil and the cathode foil, and the pores of the separator. As aresult, an improvement in the self-repairing ability of the anode foiland an increase in the electrostatic capacitance can be expected.Furthermore, cracking is unlikely to occur in the first polymercomponent even when the long constituent member on which the firstpolymer layer has been formed is spirally wound into a roll.

(4) Step of Cutting the Constituent Members (S4)

The long constituent member to which the first polymer layer has beenformed is cut after the step of forming a first polymer layer. In thiscase, the first polymer layer is not provided in each cut surface formedon the constituent member, or in other words, each end surface of theconstituent member. Other long constituent members may also be cut, forexample, in this step. The cutting step may be performed prior to thestep of producing a capacitor element or after the step of producing acapacitor element

(5) Step of Producing a Capacitor Element (S5)

A capacitor element is produced in the same manner as that of the firstembodiment is produced.

(6) Step of Impregnating the Capacitor Element with a Second DispersionLiquid (S6)

Where necessary, the capacitor element may be impregnated with a seconddispersion liquid that contains a second polymer component and a seconddispersion medium in the same manner as in the first embodiment.

(Second Dispersion Liquid)

The second dispersion liquid contains, for example, a second polymercomponent and a second dispersion medium. As the second dispersionliquid, the same as described in the first embodiment can be used.

(7) Step of Impregnating the Capacitor Element with an ElectrolyticSolution (S7)

Where necessary, the capacitor element is impregnated with anelectrolytic solution in the same manner as in the first embodiment.

(Electrolytic Solution)

The electrolytic solution contains a solvent. As the electrolyticsolution, the same as described in the first embodiment can be used.

(8) Step of Sealing the Capacitor Element (S8)

The produced capacitor element is housed into a bottomed case and sealedin the same manner as in the first embodiment

Up to here, an example has been described in which the present inventionis applied to a spirally wound electrolytic capacitor that includes acapacitor element that includes a cathode foil, but the configuration ofthe electrolytic capacitor is not limited thereto. The presentembodiment is also applicable to, for example, a stacked electrolyticcapacitor that includes a capacitor element that includes an anode foilthat includes a dielectric layer and a cathode leading layer that coversthe anode foil.

The stacked electrolytic capacitor may be produced in the followingmanner, for example.

A polymer layer is formed on both sides of an anode foil in the samemanner as descried above (S3), and then the anode foil is cut into apredetermined shape (S4). In the step of producing a capacitor element(S5), a cathode leading layer is formed so as to cover at least aportion of the conductive polymer layer formed on the surface of theanode foil.

The cathode leading layer is formed by sequentially applying thematerial of the carbon layer and a metal paste so as to cover thepolymer layer, and then performing a drying process. After that, wherenecessary, the step of impregnating the capacitor element with a seconddispersion liquid (S6) and/or the step of impregnating the capacitorelement with an electrolytic solution (S7) is performed. Finally, thecapacitor element is sealed with a resin sealant by using a moldingtechnique such as injection molding, insert molding, or compressionmolding, and an electrolytic capacitor is thereby obtained.

[Electrolytic Capacitor]

An electrolytic capacitor according to the present embodiment includes acapacitor element that includes an anode foil that includes a dielectriclayer, a cathode foil, and a separator that is interposed between theanode foil and the cathode foil, wherein a first polymer layer thatcontains a first polymer component is formed on at least one selectedfrom the group consisting of the anode foil, the cathode foil, and theseparator. The mass of the first polymer layer per unit area is 0.04mg/cm² or more.

Another electrolytic capacitor according to the present embodimentincludes a capacitor element that includes an anode foil that includes adielectric layer and a cathode leading layer that covers the anode foil,wherein a first polymer layer that contains a first polymer component isformed on the anode foil. The cathode leading layer is formed so as tocover at least a portion of the first polymer layer. The mass of thefirst polymer layer per unit area is 0.1 mg/cm² or more.

Hereinafter, the constituent members of the capacitor element and otherconstituent materials will be described.

(First Polymer Layer)

A first polymer layer that contains a first polymer component is formedon at least one constituent member. The first polymer layer is formedby, for example, applying a first dispersion liquid as described aboveto the constituent member by using a coating method. The first polymerlayer may also be formed on the outer surface of the constituent member.

The mass of the first polymer layer is not particularly limited, and maybe set as appropriate where necessary. According to the presentembodiment, the first polymer layer can be formed on the constituentmember in an amount of 0.04 mg/cm² or more per unit area. In particular,it is preferable that the first polymer layer is formed on the separatorin an amount of 0.04 mg/cm² or more. The amount of the first polymerlayer formed on the separator may be 0.1 mg/cm² or less per unit area.It is preferable that the first polymer layer is formed on each of theanode foil and the cathode foil in an amount of 0.1 mg/cm² or more. Themass of the first polymer layer formed on each of the anode foil and thecathode foil may be 1 mg/cm² or less per unit area.

The mass of the first polymer layer per unit area is calculated from thedifference in the mass of the constituent member between before andafter the application of the first dispersion liquid, or by using athermogravimetric analysis method (TGA method), as in the firstembodiment. With the TGA method, the mass of the first polymer layerattached to the constituent member can be calculated based on themeasured values.

As in the first embodiment, the electric conductivity of the firstpolymer layer may be, for example, 30 S/cm or more, or 300 S/cm or more.Even in the case where a first dispersion liquid that has a firstpolymer component concentration of 3 mass % or more is used, theelectric conductivity of the first polymer layer may be, for example,preferably 170 S/cm or less, 150 S/cm or less, or 120 S/cm or less, asin the first embodiment.

(Second Polymer Layer)

In the capacitor element, a second polymer layer as described above maybe provided, as in the first embodiment. By incorporating the secondpolymer layer, the electrostatic capacitance increases, and a reductionin the ESR can be expected. The second polymer layer is provided in thecapacitor element in an amount of, for example, 0.01 mg/cm² or more andless than 1 mg/cm².

The second polymer layer may be attached to the surface, pores, and pitsof the constituent member of the capacitor element. The second polymerlayer may be attached so as to cover at least a portion of the firstpolymer layer attached to the outer surface of the constituent member.Furthermore, the second polymer layer may be provided in the pits andpores of the constituent member to which the first polymer layer hasbeen attached.

According to the present embodiment, when the constituent member isviewed from the normal direction of the main surface of the constituentmember, for example, 50% or more of the area of the main surface iscovered by a polymer layer. The polymer layer may include the firstpolymer layer and the second polymer layer. The area coverage covered bythe polymer layer may be 60% or more, and is preferably 90% or more. Thepolymer layer may be continuous or discontinuous on the surface of theconstituent member. The polymer layer that has such a high coverage islikely to be formed when the first dispersion liquid is applied by usinga coating method. The area coverage is calculated by using the samemethod as that used in the first embodiment.

The area coverage of the surface of the constituent member covered bythe second polymer layer is smaller than the area coverage covered bythe first polymer layer. The area coverage covered by the second polymerlayer is, for example, 90% or less, or 60% or less.

The mass (density) of the first polymer layer per unit volume ispreferably higher than the mass (density) of the second polymer layer,which is formed on the first polymer layer, per unit area. The densityof the first polymer layer is calculated in the same manner as in thefirst embodiment.

(Anode Foil)

As the anode foil, the same as described in the first embodiment can beused.

In the electrolytic capacitor, a polymer layer may not be formed on theend surfaces of the anode foil. On the other hand, it is desirable thata dielectric layer is formed on the end surfaces of the anode foil.

(Cathode Foil)

As the cathode foil, the same as described in the first embodiment canbe used.

(Separator)

The separator is interposed between the anode foil and the cathode foil.

The separator is not particularly limited as long as it is porous. Asthe separator, a fiber structure such as a woven fabric, a knit, or anon-woven fabric that contains fibers may be used.

The material of the separator is not particularly limited. Examples ofthe material of the separator include: synthetic fibers such as a nylonfiber, an aramid fiber, an acrylic fiber, and a polyester fiber;cellulose; and the like. Among these, a fiber structure made ofcellulose is suitable for use as the separator because it is low costand has good affinity for the first dispersion liquid.

From the viewpoint of preventing wrinkles, the separator may be thefirst fiber structure that contains a synthetic fiber or the secondfiber structure that contains a cellulose fiber and a paperstrengthening agent used in the first embodiment

(Cathode Leading Layer)

The cathode leading layer includes, for example, a carbon layer formedso as to cover the first polymer layer and a metal paste layer formed onthe surface of the carbon layer. The carbon layer contains a conductivecarbon material such as graphite and a resin. The metal paste layercontains, for example, metal particles (for example, silver) and aresin. The configuration of the cathode leading layer is not limited tothis configuration. The configuration of the cathode leading layer isnot limited as long as it has a current collecting function.

(Resin Sealant)

The resin sealant contains, for example, a thermosetting resin. Examplesof thermosetting resin include an epoxy resin, a phenol resin, asilicone resin, a melamine resin, a urea resin, an alkyd resin,polyurethane, polyimide, an unsaturated polyester, and the like. Thematerial of the outer casing may contain a filler, a curing agent, apolymerization initiator, and/or a catalyst

FIG. 3 is a schematic cross sectional view of the electrolytic capacitoraccording to the first and second embodiments of the present embodiment.FIG. 4 is a partially exploded oblique view of a capacitor elementincluded in the electrolytic capacitor.

The electrolytic capacitor includes, for example, a capacitor element10, a bottomed case 101 that houses the capacitor element 10, a sealingmember 102 that closes an opening of the bottomed case 101, a coverplate 103 that covers the sealing member 102, lead wires 104A and 104Bthat are drawn from the sealing member 102 and pass through the coverplate 103, and lead tabs 105A and 105B that connect the lead wires toelectrodes included in the capacitor element 10. The vicinity of theopening end of the bottomed case 101 is squeezed inwardly, and theopening end is curled so as to be clumped onto the sealing member 102.

The capacitor element 10 is, for example, a spirally wound body as shownin FIG. 4. The spirally wound body includes an anode foil 11 connectedto the lead tab 105A, a cathode foil 12 connected to the lead tab 105B,and a separator 13. A first polymer layer and a second polymer layer(not shown) are formed on least one of the anode foil 11, the cathodefoil 12, and the separator 13.

The anode foil 11 and the cathode foil 12 are spirally wound with theseparator 13 interposed therebetween. The outermost layer of thespirally wound body is fixed by using a fixing tape 14. FIG. 4 is apartially exploded view of the spirally wound body before the outermostlayer of the spirally wound body is fixed by the fixing tape 14.

The electrolytic capacitor may include at least one capacitor element,or may include a plurality of capacitor elements. The number ofcapacitor elements included in the electrolytic capacitor may bedetermined according to the application purpose.

EXAMPLES

Hereinafter, the present invention will be described in further detailby way of examples. However, the present invention is not limited to theexamples given below.

Example 1

An electrolytic capacitor with a rated voltage of 35V was produced inthe manner described below

(a) Preparing Constituent Members

An aluminum foil with a thickness of 100 μm was etched so as to roughenthe surface of the aluminum foil. A chemical formation treatment wasperformed on the roughened surface of the aluminum foil to form adielectric layer, and an anode foil was thereby obtained.

An aluminum foil with a thickness of 50 μm was etched so as to roughenthe surface of the aluminum foil, and a cathode foil was therebyobtained.

A non-woven fabric with a thickness of 50 μm was prepared as the rawmaterial of the separator. The non-woven fabric was composed of 50 mass% of a synthetic fiber (compose of 25 mass % of a polyester fiber and 25mass % of an aramid fiber), and 50 mass % of cellulose, and containedpolyacrylamide serving as a paper strengthening agent. The non-wovenfabric had a density of 0.35 g/cm³.

(b) Preparing a First Dispersion Liquid

A mixed solution was prepared by dissolving 3,4-ethylenedioxythiopheneand polystyrene sulfonic acid (PSS with a weight-average molecularweight of 100,000) in ion exchanged water. Iron sulfate (III) (servingas an oxidizing agent) was added in the mixed solution being stirred,and thereby a polymerization reaction was performed. After that, thereaction solution was dialyzed so as to remove unreacted monomers andthe oxidizing agent, and a first dispersion liquid A containingpolyethylenedioxythiophene (PEDOT/PSS serving as a first polymercomponent) doped with about 5 mass % of PSS (serving as a dopant) wasthereby obtained.

The concentration of the first polymer component in the first dispersionliquid A was 2 mass %. The viscosity of the first dispersion liquid Ameasured at room temperature (20° C.) by using a vibration viscometer(VM-100A available from Sekonic Corporation) was 40 mPa·s.

(c) Forming a First Polymer Layer (Producing a Separator)

The first dispersion liquid A was applied to both sides of the fiberstructure by using a gravure coater. After that, a drying process wasperformed, and a separator including the first polymer layer was therebyobtained. The mass of the first polymer layer per unit area of theseparator was 0.02 mg/cm². The area coverage of one of the main surfacesof the separator covered by the first polymer layer was 98%. Theelectric conductivity of the first polymer layer was 400 S/cm.

(d) Producing a Capacitor Element

The anode foil, the cathode foil, and the separator were cut intopredetermined sizes.

An anode lead tab and a cathode lead tab were connected to the anodefoil and the cathode foil, and the anode foil and the cathode foil werespirally wound with the separator interposed therebetween together withthe lead tabs. An anode lead wire and a cathode lead wire were connectedto the end portions of the lead tabs protruding from the spirally woundbody, respectively. A chemical formation treatment was again performedon the obtained spirally wound body, and a dielectric layer was formedon the end surfaces of the anode foil. The end portion of the outersurface of the spirally wound body was fixed using a fixing tape, and acapacitor element was thereby obtained.

(e) Preparing a Second Dispersion Liquid and Impregnation

A mixed solution was prepared by dissolving 3,4-ethylenedioxythiopheneand polystyrene sulfonic acid (PSS with a weight-average molecularweight of 100,000) in ion exchanged water. Iron sulfate (III) (servingas an oxidizing agent) was added in the mixed solution being stirred,and thereby a polymerization reaction was performed. After that, thereaction solution was dialyzed so as to remove unreacted monomers andthe oxidizing agent, and a second dispersion liquid containingpolyethylenedioxythiophene (PEDOT/PSS serving as a second polymercomponent) doped with about 5 mass % of PSS (serving as a dopant) wasthereby obtained.

The concentration of the second polymer component in the seconddispersion liquid was 1.5 mass %. The viscosity of the second dispersionliquid measured at room temperature (20° C.) by using a vibrationviscometer (VM-100A available from Sekonic Corporation) was 30 mPa·s.

The capacitor element was immersed in the second dispersion liquid underreduced atmosphere (40 kPa) for five minutes, and then subjected to adrying process. A second polymer layer was thereby formed.

(f) Impregnation with an Electrolytic Solution

Ethylene glycol (EG) was prepared as a solvent. An electrolytic solutionwas prepared by dissolving, in EG, 5-sulfosalicylic acid (divalent acidcomponent) serving as a second sulfonic acid and trimethylamine servingas a basic component at a concentration of 25 mass % in total. Theequivalence ratio of 5-sulfosalicylic acid relative to triethylamine wasset to 2.0.

The capacitor element was immersed in the electrolytic solution underreduced atmosphere (40 kPa) for five minutes after the capacitor elementhad been impregnated with the second dispersion liquid.

(g) Sealing the Capacitor Element

The capacitor element impregnated with the electrolytic solution wassealed, and an electrolytic capacitor (Al) as shown in FIG. 3 wasobtained. After that, the capacitor element was subjected to aging at95° C. for 90 minutes while applying the rated voltage.

<Evaluation>

The electrolytic capacitor Al that had been subjected to aging wasmeasured for electrostatic capacitance and ESR (with the measurementtemperature being set to 20° C.). The evaluation results are shown asrelative values with respect to the electrostatic capacitance and theESR of an electrolytic capacitor B1 produced in Comparative Example 1.

After the electrostatic capacitance and the ESR had been measured, theelectrolytic capacitor Al was disassembled, and each constituent memberwas taken out therefrom. The mass of the second polymer layer per unitarea in the entire capacitor element was 0.07 mg/cm². The area coverageof one of the main surfaces of the separator covered by the secondpolymer layer was 83%.

Furthermore, a cross section of the separator was observed by using anSEM, and the mass of the first polymer layer per unit area and the massof the second polymer layer per unit area were calculated. The mass ofthe first polymer layer per unit area was higher than the mass of thesecond polymer layer per unit area.

Example 2

An electrolytic capacitor A2 was produced in the same manner as inExample 1, except that, in the step (c) of forming a first polymerlayer, the first dispersion liquid A was also applied to both sides ofthe anode foil by using a gravure coater in addition to the fiberstructure, and the produced electrolytic capacitor was evaluated in thesame manner. The results are shown in Table 1.

The mass of the first polymer layer formed on the anode foil per unitarea was 0.3 mg/cm². The area coverage of one of the main surfaces ofthe anode foil covered by the first polymer layer was 99%.

Example 3

An electrolytic capacitor A3 was produced in the same manner as inExample 1, except that, in the step (c) of forming a first polymerlayer, the first dispersion liquid A was also applied to both sides ofthe cathode foil by using a gravure coater in addition to the fiberstructure, and the produced electrolytic capacitor was evaluated in thesame manner. The results are shown in Table 1. The mass of the firstpolymer layer formed on the cathode foil per unit area was 0.3 mg/cm².The area coverage of one of the main surfaces of the cathode foilcovered by the first polymer layer was 99%.

Comparative Example 1

An electrolytic capacitor B1 was produced in the same manner as inExample 1, except that the step (c) of forming a first polymer layer wasnot performed, and the produced electrolytic capacitor was evaluated inthe same manner. The results are shown in Table 1.

TABLE 11 Electrostatic Electrolytic capacitor capacitance ESR A1 1.010.96 A2 1.01 0.94 A3 1.02 0.93 B1 1 1

Example 4

A first dispersion liquid B was prepared in the same manner as inExample 1, except that, in the step (b) of preparing a first dispersionliquid, PSS with a weight-average molecular weight of 50,000 was used.The concentration of the first polymer component in the first dispersionliquid B was 4 mass %. The viscosity of the first dispersion liquid Bmeasured at room temperature (20° C.) by using a vibration viscometer(VM-100A available from Sekonic Corporation) was 105 mPa·s.

An electrolytic capacitor A4 was produced in the same manner as inExample 1, except that the first dispersion liquid B was used, and theproduced electrolytic capacitor was evaluated in the same manner. Theresults are shown in Table 1.

The mass of the first polymer layer formed on the separator per unitarea was 0.04 mg/cm². The area coverage of one of the main surfaces ofthe separator covered by the first polymer layer was 98%. The electricconductivity of the first polymer layer was 150 S/cm. The area coverageof one of the main surfaces of the separator covered by the secondpolymer layer was 83%.

Example 5

An electrolytic capacitor A5 was produced in the same manner as inExample 2, except that the first dispersion liquid B was used, and theproduced electrolytic capacitor was evaluated in the same manner. Theresults are shown in Table 2.

The mass of the polymer layer formed on the anode foil per unit area was0.4 mg/cm², and the mass of the polymer layer formed on the separatorper unit area was 0.04 mg/cm². The area coverage of one of the mainsurfaces of the anode foil covered by the first polymer component was99%, and the area coverage of one of the main surfaces of the separatorcovered by the first polymer layer was 98%. The area coverage of one ofthe main surfaces of each of the anode foil and the separator covered bythe second polymer component was 83%.

Example 6

An electrolytic capacitor A6 was produced in the same manner as inExample 3, except that the first dispersion liquid B was used, and theproduced electrolytic capacitor was evaluated in the same manner. Theresults are shown in Table 2.

The mass of the first polymer layer formed on the cathode foil per unitarea was 0.4 mg/cm², and the mass of the first polymer layer formed onthe separator per unit area was 0.04 mg/cm². The area coverage of one ofthe main surfaces of the cathode foil covered by the first polymercomponent was 99%, and the area coverage of one of the main surfaces ofthe separator covered by the first polymer layer was 98%. The areacoverage of one of the main surfaces of each of the cathode foil and theseparator was 83%.

Example 7

An electrolytic capacitor A7 was produced in the same manner as inExample 4, except that, in the step (c) of forming a first polymerlayer, the first dispersion liquid B was also applied to both sides ofeach of the anode foil and the cathode foil by using a gravure coater inaddition to the fiber structure, and the produced electrolytic capacitorwas evaluated in the same manner. The results are shown in Table 2.

The mass of the first polymer layer formed on each of the anode foil andthe cathode foil per unit area was 0.4 mg/cm², and the mass of the firstpolymer layer formed on the separator per unit area was 0.04 mg/cm². Thearea coverage of one of the main surfaces of each of the anode foil andthe cathode foil covered by the first polymer layer was 99%, and thearea coverage of one of the main surfaces of the separator covered bythe first polymer layer was 98%. The area coverage of one of the mainsurfaces of each of the anode foil, the cathode foil, and the separatorcovered by the second polymer layer was 83%.

TABLE 2 Electrostatic Electrolytic capacitor capacitance ESR A4 1.010.94 A5 1.01 0.91 A6 1.03 0.91 A7 1.04 0.87 B1 1 1

Example 8

An electrolytic capacitor A8 was produced in the same manner as inExample 1, except that, as the raw material of the separator, a 90 μmthick non-woven fabric (with a density of 0.35 g/cm³) containing 50 mass% of a synthetic fiber (composed of 25 mass % of a polyester fiber and25 mass % of an aramid fiber) and 50 mass % of cellulose, andpolyacrylamide serving as a paper strengthening agent was used, and theproduced electrolytic capacitor was evaluated in the same manner. Theresults are shown in Table 3. The evaluation results are shown asrelative values with respect to the electrostatic capacitance and theESR of an electrolytic capacitor B2 produced in Comparative Example 2.The area coverage of one of the main surfaces of the separator coveredby the first polymer layer was 99%.

After the electrostatic capacitance and the ESR had been measured, theelectrolytic capacitor A8 was disassembled, and each constituent memberwas taken out therefrom. The mass of the second polymer layer per unitarea in the entire capacitor element was 0.07 mg/cm². The area coverageof one of the main surfaces of the separator covered by the secondpolymer layer was 83%.

Furthermore, a cross section of the separator was observed by using anSEM, and the mass of the first polymer layer per unit area and the massof the second polymer layer per unit area were calculated. The mass ofthe first polymer layer per unit area was higher than the mass of thesecond polymer layer per unit area.

Comparative Example 2

An electrolytic capacitor B2 was produced in the same manner as inExample 8, except that the first dispersion liquid was not applied tothe fiber structure, and the produced electrolytic capacitor wasevaluated in the same manner. The results are shown in Table 3.

TABLE 3 Electrostatic Electrolytic capacitor capacitance ESR A8 1.011.98 B2 1 2.05

Example 9

A capacitor element and an electrolytic capacitor A9 were produced inthe same manner as in Example 1, except that, in the step (c) of forminga first polymer layer, the first dispersion liquid B prepared in Example4 was applied to both sides of the anode foil instead of the fiberstructure, and the produced electrolytic capacitor was evaluated in thesame manner. The results are shown in Table 4.

The mass of the first polymer layer per unit area was 0.4 mg/cm². Thearea coverage of one of the main surfaces of the anode foil covered bythe first polymer layer was 99%. The electric conductivity of the firstpolymer layer was 150 S/cm. The mass of the second polymer layer perunit area in the entire capacitor element was 0.07 mg/cm². The areacoverage of one of the main surfaces of the anode foil covered by thesecond polymer layer was 83%.

Furthermore, a cross section of the anode foil was observed by using anSEM, and the mass of the first polymer layer per unit area and the massof the second polymer layer per unit area were calculated. The mass ofthe first polymer layer per unit area was higher than the mass of thesecond polymer layer per unit area.

Example 10

A capacitor element and an electrolytic capacitor A10 were produced inthe same manner as in Example 1, except that, in the step (c) of forminga first polymer layer, the first dispersion liquid B prepared in Example4 was applied to both surfaces of the cathode foil instead of the fiberstructure, and the produced electrolytic capacitor was evaluated in thesame manner. The results are shown in Table 4.

The mass of the first polymer layer formed on the cathode foil per unitarea was 0.4 mg/cm². The area coverage of one of the main surfaces ofthe cathode foil covered by the first polymer layer was 99%. The areacoverage of one of the main surfaces of the cathode foil covered by thesecond polymer layer was 83%.

Example 11

A capacitor element and an electrolytic capacitor A11 were produced inthe same manner as in Example 1, except that, in the step (c) of forminga first polymer layer, the first dispersion liquid B prepared in Example4 was applied to both sides of each of the anode foil and the cathodefoil instead of the fiber structure, and the produced electrolyticcapacitor was evaluated in the same manner. The results are shown inTable 4.

The mass of the polymer layer formed on each of the anode foil and thecathode foil per unit area was 0.4 mg/cm². The area coverage of one ofthe main surfaces of each of the anode foil and the cathode foil coveredby the first polymer component was 99%. The area coverage of one of themain surfaces of each of the anode foil and the cathode foil covered bythe second polymer component was 83%.

TABLE 4 Electrostatic Electrolytic capacitor capacitance ESR A9  1.010.93 A10 1.03 0.92 A11 1.03 0.90 B1  1 1

Industrial Applicability

The present invention is suitable particularly for use in anelectrolytic capacitor through which a high ripple current flows.

The present invention has been described in terms of the presentlypreferred embodiments, but the disclosure should not be interpreted aslimiting. Various alterations and modifications will no doubt becomeapparent to those skilled in the art to which the invention pertains,after having read the disclosure. Accordingly, it is to be understoodthat the appended claims be interpreted as covering all alterations andmodifications which fall within the true spirit and scope of the presentinvention.

REFERENCE SIGNS LIST

100: electrolytic capacitor

101: bottomed case

102: sealing member

103: cover plate

104A, 104B: lead wire

105A, 105B: lead tab

10: capacitor element

-   -   11: anode foil    -   12: cathode foil    -   13: separator    -   14: fixing tape

1. A method for producing an electrolytic capacitor, the methodcomprising the steps of: preparing an anode foil that includes adielectric layer, a cathode foil, and a fiber structure; preparing aconductive polymer dispersion liquid that contains a conductive polymercomponent and a dispersion medium; producing a separator by applying theconductive polymer dispersion liquid to the fiber structure and thenremoving at least a portion of the dispersion medium; and producing acapacitor element by sequentially stacking the anode foil, theseparator, and the cathode foil, wherein the dispersion medium containswater, the fiber structure contains a synthetic fiber in an amount of 50mass % or more, and the fiber structure has a density of 0.2 g/cm³ ormore and less than 0.45 g/cm³.
 2. The method for producing anelectrolytic capacitor in accordance with claim 1, wherein the syntheticfiber comprises at least one selected from the group consisting of anylon fiber, an aramid fiber, an acrylic fiber, and a polyester fiber.3. The method for producing an electrolytic capacitor in accordance withclaim 1, wherein the fiber structure contains a cellulose fiber in anamount of 10 mass % or more and less than 50 mass %.
 4. A method forproducing an electrolytic capacitor, the method comprising the steps of:preparing an anode foil that includes a dielectric layer, a cathodefoil, and a fiber structure; preparing a conductive polymer dispersionliquid that contains a conductive polymer component and a dispersionmedium; producing a separator by applying the conductive polymerdispersion liquid to the fiber structure and then removing at least aportion of the dispersion medium; and producing a capacitor element bysequentially stacking the anode foil, the separator, and the cathodefoil, wherein the dispersion medium contains water, the fiber structurecontains 40 mass % or more of a cellulose fiber and a paperstrengthening agent, and the fiber structure has a density of 0.2 g/cm³or more and less than 0.45 g/cm³.
 5. The method for producing anelectrolytic capacitor in accordance with claim 4, wherein the paperstrengthening agent comprises at least one selected from the groupconsisting of a urea formaldehyde resin, a melamine formaldehyde resin,a polyamide polyamine epichlorohydrin, and a polyvinylamine.
 6. Themethod for producing an electrolytic capacitor in accordance with claim4, wherein the paper strengthening agent comprises at least one selectedfrom the group consisting of a polyacrylamide, a polyvinyl alcohol, astarch, and a carboxymethyl cellulose.
 7. The method for producing anelectrolytic capacitor in accordance with claim 4, wherein the fiberstructure contains a synthetic fiber.
 8. The method for producing anelectrolytic capacitor in accordance with claim 1, wherein, in the stepof producing the separator, the conductive polymer dispersion liquid isapplied to the fiber structure by using a coating method.
 9. The methodfor producing an electrolytic capacitor in accordance with claim 1,wherein the conductive polymer component is contained in the conductivepolymer dispersion liquid in an amount of 1 mass % or more and 15 mass %or less, and the conductive polymer dispersion liquid has a viscosity of10 mPa·s or more, the viscosity being measured at room temperature byusing a vibration viscometer.
 10. An electrolytic capacitor comprising:an anode foil that includes a dielectric layer; a cathode foil; and aseparator that is interposed between the anode foil and the cathodefoil, wherein the separator contains a fiber structure and a conductivepolymer component that is attached to the fiber structure, the fiberstructure contains a synthetic fiber in an amount of 50 mass % or more,and the fiber structure has a density of 0.2 g/cm³ or more and less than0.45 g/cm³.
 11. An electrolytic capacitor comprising: an anode foil thatincludes a dielectric layer; a cathode foil; and a separator that isinterposed between the anode foil and the cathode foil, wherein theseparator contains a fiber structure and a conductive polymer componentthat is attached to the fiber structure, the fiber structure contains 40mass % or more of a cellulose fiber and a paper strengthening agent, andthe fiber structure has a density of 0.2 g/cm³ or more and less than0.45 g/cm³.
 12. The electrolytic capacitor in accordance with claim 10,wherein a mass of the conductive polymer component per unit area of theseparator is 0.02 mg/cm² or more.
 13. A conductive polymer dispersionliquid that is to be applied to a sheet-like member that constitutes acapacitor element by using a coating method, the conductive polymerdispersion liquid comprising: a conductive polymer component; and adispersion medium, wherein the conductive polymer component is containedin an amount of 3 mass % or more and 15 mass % or less, and theconductive polymer dispersion liquid has a viscosity of 100 mPa·s ormore, the viscosity being measured at room temperature by using avibration viscometer.
 14. The conductive polymer dispersion liquid inaccordance with claim 13, wherein the viscosity is 200 mPa·s or less.15. The conductive polymer dispersion liquid in accordance with claim13, wherein the conductive polymer component contains a polyanion, andthe polyanion has a weight-average molecular weight of 1,000 or more and70,000 or less.
 16. A method for producing an electrolytic capacitor,the method comprising the steps of: Preparing a sheet-like member thatconstitute a capacitor element; preparing a first conductive polymerdispersion liquid that contains a first conductive polymer component anda first dispersion medium, wherein the first conductive polymercomponent is contained in an amount of 3 mass % or more and 15 mass % orless, and the first conductive polymer dispersion liquid has a viscosityof 100 mPa·s or more, the viscosity being measured at room temperatureby using a vibration viscometer; forming a conductive polymer layer thatcontains the first conductive polymer component by applying the firstconductive polymer dispersion liquid to the sheet-like member by using acoating method and then removing at least a portion of the firstdispersion medium; and producing a capacitor element by using thesheet-like member on which the conductive polymer layer has been formed.17. The method for producing an electrolytic capacitor in accordancewith claim 16, wherein the viscosity of the first conductive polymerdispersion liquid is 200 mPa·s or less.
 18. The method for producing anelectrolytic capacitor in accordance with claim 16, wherein the firstconductive polymer component contains a polyanion, and the polyanion hasa weight-average molecular weight of 1,000 or more and 70,000 or less.19. The method for producing an electrolytic capacitor in accordancewith claim 16, comprising the step of impregnating the producedcapacitor element with an electrolytic solution.
 20. The method forproducing an electrolytic capacitor in accordance with claim 16,comprising the step of impregnating the produced capacitor element witha second conductive polymer dispersion liquid, wherein the secondconductive polymer dispersion liquid contains a second conductivepolymer component and a second dispersion medium, the second conductivepolymer component is contained in an amount of 0.5 mass % or more andless than 3 mass %, and the second conductive polymer dispersion liquidhas a viscosity of less than 100 mPa·s, the viscosity being measured atroom temperature by using a vibration viscometer.
 21. The method forproducing an electrolytic capacitor in accordance with claim 16,wherein, in the step of forming a conductive polymer layer, theconductive polymer layer that contains the first conductive polymercomponent and the first dispersion medium is formed by removing aportion of the first dispersion medium.
 22. An electrolytic capacitorcomprising a capacitor element that includes: an anode foil thatincludes a dielectric layer; a cathode foil; and a separator that isinterposed between the anode foil and the cathode foil, wherein aconductive polymer layer that contains a first conductive polymercomponent is formed on at least one selected from the group consistingof the anode foil, the cathode foil, and the separator, and a mass ofthe conductive polymer layer per unit area is 0.04 mg/cm² or more. 23.The electrolytic capacitor in accordance with claim 22, wherein theconductive polymer layer has an electric conductivity of 170 S/cm orless.
 24. The method for producing an electrolytic capacitor inaccordance with claim 4, wherein, in the step of producing theseparator, the conductive polymer dispersion liquid is applied to thefiber structure by using a coating method.
 25. The method for producingan electrolytic capacitor in accordance with claim 4, wherein theconductive polymer component is contained in the conductive polymerdispersion liquid in an amount of 1 mass % or more and 15 mass % orless, and the conductive polymer dispersion liquid has a viscosity of 10mPa·s or more, the viscosity being measured at room temperature by usinga vibration viscometer.
 26. The electrolytic capacitor in accordancewith claim 11, wherein a mass of the conductive polymer component perunit area of the separator is 0.02 mg/cm² or more.